Implement interruptible ECC export-public

[gilles-peskine-arm]

Implement and test interruptible export-public-key functions as specfied in ARM-software/psa-api#199 :

psa_status_t psa_export_public_key_iop_abort(psa_export_public_key_iop_t * operation);
psa_status_t psa_export_public_key_iop_complete(psa_export_public_key_iop_t * operation,
                                                uint8_t * data,
                                                size_t data_size,
                                                size_t * data_length);
uint32_t psa_export_public_key_iop_get_num_ops(psa_export_public_key_iop_t * operation);
psa_export_public_key_iop_t psa_export_public_key_iop_init(void);
psa_status_t psa_export_public_key_iop_setup(psa_export_public_key_iop_t * operation,
                                             psa_key_id_t key);

The scope of this issue is:

• The functions work for all key pair and public-key types.
• For RSA and DH, complete() returns on the first call.
• For ECC, complete() is interruptible according to the iop setting.
• Unit test to the usual coverage level.

[paul-elliott-arm]

Given we don't support RSA / DH keys for any other interruptible operation, I think for the first version, given how short we are on time I would just implement ECC keys for now. The others can be added later when we have more time - its not the implementation that is going to take time here, but all the testing and extended testing that this will bring in, and we are already over time.

[gilles-peskine-arm]

I think for the first version, given how short we are on time I would just implement ECC keys for now.

Good point, in the first pass we should focus on what we need for X.509/TLS. Those modules go through pk. So we can do the selection of interruptible APIs in pk, which requires less testing because it'll be oriented towards how it's eventually used in X.509/TLS and we don't need much testing beyond what's covered by the X.509/TLS usage.

[paul-elliott-arm]

Closing this as we are splitting it into 5 parts:

PSA Headers : #9646
Setup and Abort Functions : #9647
Complete function and full tests: #9648
IOP based functions and tests: #9649
Driver wrappers: #9650